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  <section id="cmp0174">
<span id="policy:CMP0174"></span><h1>CMP0174<a class="headerlink" href="#cmp0174" title="Link to this heading">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.31.</span></p>
</div>
<p><span class="target" id="index-0-command:cmake_parse_arguments"></span><a class="reference internal" href="../command/cmake_parse_arguments.html#command:cmake_parse_arguments" title="cmake_parse_arguments(parse_argv)"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_parse_arguments(PARSE_ARGV)</span></code></a> defines a variable for an empty
string after a single-value keyword.</p>
<p>One of the main reasons for using the <code class="docutils literal notranslate"><span class="pre">PARSE_ARGV</span></code> form of the
<span class="target" id="index-1-command:cmake_parse_arguments"></span><a class="reference internal" href="../command/cmake_parse_arguments.html#command:cmake_parse_arguments" title="cmake_parse_arguments"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_parse_arguments()</span></code></a> command is to more robustly handle corner
cases related to empty values.  The non-<code class="docutils literal notranslate"><span class="pre">PARSE_ARGV</span></code> form doesn't preserve
empty arguments, but the <code class="docutils literal notranslate"><span class="pre">PARSE_ARGV</span></code> form does.  For each single-value
keyword given, a variable should be defined if the keyword is present, even
if it is followed by an empty string.</p>
<p>Prior to CMake 3.31, no variable would be defined if the value given after a
single-value keyword was an empty string.  This meant the code could not detect
the difference between the keyword not being given, and it being given but with
an empty value, except by iterating over all the arguments and checking if the
keyword is present.</p>
<p>For the <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of this policy,
<span class="target" id="index-2-command:cmake_parse_arguments"></span><a class="reference internal" href="../command/cmake_parse_arguments.html#command:cmake_parse_arguments" title="cmake_parse_arguments(parse_argv)"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_parse_arguments(PARSE_ARGV)</span></code></a> does not define a variable for a
single-value keyword followed by an empty string, or followed by no value at
all.</p>
<p>For the <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior, <span class="target" id="index-3-command:cmake_parse_arguments"></span><a class="reference internal" href="../command/cmake_parse_arguments.html#command:cmake_parse_arguments" title="cmake_parse_arguments(parse_argv)"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_parse_arguments(PARSE_ARGV)</span></code></a> always
defines a variable for each keyword given in the arguments, even a single-value
keyword with an empty string as its value or no value at all.  With the
<code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior, the code can robustly check if a single-value keyword was
given using just <code class="docutils literal notranslate"><span class="pre">if(DEFINED</span> <span class="pre">&lt;prefix&gt;_&lt;keyword&gt;)</span></code>.</p>
<p>This policy was introduced in CMake version 3.31.
It may be set by <span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> or <span class="target" id="index-0-command:cmake_minimum_required"></span><a class="reference internal" href="../command/cmake_minimum_required.html#command:cmake_minimum_required" title="cmake_minimum_required"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_minimum_required()</span></code></a>.
If it is not set, CMake warns, and uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is
<span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a>
and may be removed in a future version of CMake.</p>
</div>
</section>


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